Relay



June 15, 1943. A. G. STIMSON RELAY Filed April 18, 1942 n z 5 m n V A A my W HM M v Patented June' 15, 1943 RELAY Allen G. Stimson, Lynnfield, Mass, assignor to General Electric Company, a corporation of New York Application April 18, 1942, Serial No. 439,508

Claims.

My invention relates to relays and more specifically to overload relays of the type having a thermo-sensitive magnetizable portion responsive to heat generated by a current flowing in the circult to be protected.

A number of thermo-sensitive magnetic materials having the property of changing their magnetic permeability in a nonlinear manner with changes in temperature are well known to those skilled in the art. Certain metal al oys have this property to a marked degree, notably certain alloys of nickel,' such as nickel-copper and nickel-iron alloy.

In the application of such an alloy to electric relays there are certain inherent difliculties which must be eitherovercome-or minimized. In the first place, thermo-magnetic alloys are at best only about one-half as permeable as soft iron. Furthermore, while the total change of permeability with temperature is sufliciently large to be effective, the maximum rate of change is not sufliciently rapid to produce the desired speed of relay operation. My overload relay, while simple and rugged in structure, is inexpensive to manufacture and minimizes the adverse effects of the above properties of thermo-magnetic material.

Accordingly it is an object of my invention to provide an electric overload relay of the thermomagnetic type which shall be inexpensive to manufacture, of simpleand rugged construction, and efllcient, reliable and durable in operation.

It is a further object of my invention to provide an electric overload relay using inexpensive thermo-magnetic wire as the temperature sensitive element;

It is a still further object of my invention to provide an electric overload relay having a special type snap action for operation in conjunction with a sensitive element consisting of thermo-' magnetic wire.

According to a preferred form of my invention, I provide a movable switch member including a small permanent magnet of relatively high coercive force in combination with a fixed keeper formed of a closely wound coil of thermo-magnetic wire having convolutions so disposed that at least a portion of each convolution lies longitudinally in the path of magne ic flux between the pole faces of the magnet. Means are provided for biasing the permanent magnet to a contact dise agi g position-but under normal operat ing conditions the biasing force is resisted and the magnet relea-sably retained in a contact engaging position by the magnetic attraction of the magnet for its thermo-magnetic current carrying keeper coil.

For a more complete understanding of my invention and a further appreciation of its objects and advantages, reference should now be had to the following detailed specification taken in conjunction with the accompanying drawing in which Fig. 1 is a side elevation of an overload relay embodying my invention, certain parts being broken away to show the internal structure:

Fig. 2 is a cross-sectional view taken along the line 22 of Fig. 1; Fig. 3 is a plan view of the device of Fig. 1; Fig. 4 is a perspective view of the permanent magnet and thermo-magnetic keeper; and Fig. 5 is a cross-sectional view of an electric overload relay embodying the principles of my invention in a modified form.

Referring now to the drawing. and particularly to Figs. 1 to 4 inclusive, my overload relay in one form comprises a hollow substantially cylindrical casing ll) of suitable insulating material, such as a molded plastic compound, provided at one end with a removable circular closure plate H of insulating material and formed exteriorly to pro-'- vide a plurality of pairs of radially extending bosses l2 and I3. The circular end plate II is held against outward displacement by a plurality of radially inwardly extending ears H formed upon the casing Ill and is manually movable longitudinally inwardly of the casing ill to serve asa reset button in a manner to be more'fully explained hereinafter. The pair of external bosses I2 is fitted with a pair of terminal connectors which provide external electrical connection to a pair of stationary contact members IS.

The cylindrical casing I0 is slotted longitudinally, as at I1. and I8, slidably to accommodate a diametrically disposed bridging contact I! which is normally biased into engagement with the fixed contacts l6 by a relatively light compression spring disposed between the bridging contact l9 and the end plate H of the relaycasing. Beneath the bridging contact 19 there is slidably mounted within the casing II a small permanent magnet having attached at one end thereof, as by a bolt 25, an overhanging circular cap 21 of insulating material. Thus the spring 20 maintains the bridging contact is constantly in following engagement with the magnet 25. A helical compression spring 28 surrounding the magnet 25 and disposed between an annular shoulder 29 on the cap 21 and an annular shoulder 30 formed on the casing l0 biases the entire movable switch member, comprising the magnet 25, cap 21 and the bridging contact ill, to a. contact disengaging position against the biasing force of the relatively light followup spring 20.

As best shown at Fig. 4. the permanent magnet 25 is of substantially cylindrical configuration having one end slotted diametrically as at 25a. Adjacent sides of the magnet are oppositely magnetized in the manner of a U-shaped or horseshoe magnet thereby forming a. pair of substantially semicircular pole faces 25?) and 250 of opposite polarity lying in the same plane. In order to obtain suflicient coercive force while limiting the physical proportions ofthe magnet, I prefer to formthe magnet 25 of an alloy comprising 6 to 15% aluminum. 12 to 30% nickel, about 5% copper, if desired, and the remainder of iron, such as described and claimed in Patents 1,947,274 and 1,968,569, issued February 19 and July 31, 1934, respectively, to William E. Ruder.

Each of the pair of external bosses I3 on the casing I ll is fitted with a cylindrical externally knurled and internally threaded bushing 3i arranged to support a fiat coil spool 32 at the open end of the casing l in parallel spaced relation to the plane 01' the pole faces 25b and 250 of the ing ends of a pair of electrically conducting metal plates 35 which are inset in the bosses l3 and riveted to the bushings M. The bolts 38 which serve to mount the spool 32 also clamp a pair of lead wires 34a and 34b from the coil 34 between the plates 35 and the lobes oi the spool 32.

The coil 34 which is preferably substantially flat, is best illustrated at Fig. 4, and is formed of a plurality of closely wound convolutlcns of thermo-magnetic wire which has the property of undergoing a nonlinear decrease of magnetic permeability as its temperature is increased. In order to insure minimum reluctance between the pole faces 25b and 25c of the permanent magnet the coil 34 is preferably mounted for direct engagement with the pole faces to serve as a fixed magnet keeper and is so disposed that one of the longer sides of each turn or convolution of the coil lies substantially longitudinally of the path of magnetic flux between the pole faces of the magnet when the magnet is in its contact engaging position.

From the foregoing detailed description of the various elements of my device and the manner of their assembly, it is believed that the mode of operation will be evident from the following brief description.

Referring particularly to Figs. 1 and 2, the relay is shown with the movable switch member in its normal or circuit closing position wherein the permanent magnet 25 is magnetically retained in engagement with the keeper coil 34 against the circuit opening bias of the compression spring 28.. It will be understood that current of a load circuit to be protected or a current proportional thereto is passed through the thermo-magnetic keeper coil 34 by connection of the circuit to the terminal connectors 33, and that the contacts l6 and 19 are connected through the terminal connectors 15 in a suitable manner to enable them to disable the load circuit upon their disengagement. I1 now the current in the load circuit and, consequently the current traversing the keeper coil 34, exceeds a predetermined excessive value the heat generated in the coil 34 will be sufficient to cause a marked and relative-. ly rapid decrease in the permeability of the coil 34 so that the force of magnetic attraction between the coil 34 and the permanent magnet 25 will diminish to a point where it is exceeded by the biasing force of the compression spring II. Since the spring 20 also opposes the spring 2|, it will be evident that the force of magnetic attraction must decrease to a point where the sum of the magnetic force and the force of the spring 20 is less than the force of the spring 28. Under such conditions the spring 23 will disengage the magnet 25 from the keeper coil 34 and will move the magnet and bridging contact I9 quickly to a circuit opening position. In order that this operation might be carried out with the desired snap action, it is necessary that the gradient of the spring 20 be less than the combined gradient of the spring 28 and the force of magnetic attraction, If the spring 20 is too stiff the opening movement 'will take place slowly.

The relay as described inherently tends to reset automatically, since a decrease in temperature oi the keeper coil 34 increases its permitability and increases the magnetic attraction between it and the magnet 25. It has been found preferable, however, to forego the advantages or automatic resetting operation by operating the device on a differential too wide to permit resetting, thereby to obtain a more dependable snap action upon contact disengaging movement. It is to provide for manual resetting that I have arranged the end plate H of the casing ll ior inward movement against the combined force of the compression springs 20 and 28. By pressing the end plate H inwardly the magnet 25 is forced into engagement with the keeper coil 34 and, it this coil has cooled sufficiently, the force of magnetic attraction between the coil and the magnet will maintain the magnet in its contact engaging position.

At Fig. 5 I have shown a modified form of my invention in which'a permanent magnet 53 is resiliently and pivotally mounted upon a leaf spring St for movement through an aperture I2 in a base 53 of suitable insulating material. The leaf spring 5! is mounted upon a relatively rigid supporting bracket 54 and is biased to a circuit opening position by a light spring strip 55. At one end the leaf spring 51 carries a movable contact 56 for engagement with a stationary contact 51, and intermediate its ends is mounted a permanent magnet 50 set in a molded cup 53 of suitable insulating material which serves to insulate the magnet 58 from the contact spring 5i. On the under side'of the base 53 and opposite the leaf spring Si is rigidly mounted a fiat spool d9 of insulating material which serves to support a keeper coil 50 formed of a plurality of convolutions of 'thermomagnetic wire. As previously described in connection with the device of Fig. 1, the conv olutions of the coil 50 are so disposed with relation to the poles of the magnet 50 that at least one of the longer sides of each turn or convolution forms a part of and extends in the direction of the magnetic path between the pole faces of the magnet 50. The device of Fig. 5 functions in substantially the same manner as that of Fig. l, and it is believed that its mode of operation will be sufficiently clear from the previous description with reference to Fig. 1.

While I have shown and described certain preferred embodiments of my invention by way of illustration, many other modifications will be apparent to those skilled in the art, and I, therefore, wish to have it understood that I desire by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

asaaooo' 7 contact mounted for actuation by said magnet What I claim vas new and desire to secure by Letters Patent of the United States is:

1. An overload relay comprising in combination, a hollow cylindrical base of insulating material closed at one end, fixed contacts mounted upon saidbase, a movable bridging contact extending diametrically of said base, a U-shap'ed permanent magnet slidably mounted within said base to actuate said bridging contact, spring- 'netic permeability, whereby with loss of permeability said keeper releases said magnet with a of insulating material fixedly attached to said- 1 base and disposed opposite the closed end thereof normally to engage the pole faces of said magnet as a keeper for releasably retaining said magnet in a contact engaging position, said coil comprising a plurality of convolutions one of the longer sides of each of which extends substantially longitudinally of the path or magnetic flux between said pole faces when said magnet is in said contact engaging position, and means for supplying electric current to said coil to heat said wire, whereby with loss of magnetic permeability said keeper coil releases said magnet with a snap action to disengage said contacts; I p

-2. An overload relay comprising in combination, a hollow cylindrical base ofinsulating material, a pair of fixed contacts mounted upon bosses formed exterially of said base, a manually operable reset button forming adisc-shaped end wall forsaidj cylindrical base, said reset button being movable into said cylindrical base and being provided with stops limiting outward movement thereof, a movable bridging contact diametrically disposed with respect to said cylindrical base to engage said fixed contacts, said.

bridging contact being slidable longitudinally of said base, a U-shaped permanent magnet slidably mounted within said base, a compression spring disposed between said bridging contact and said reset button to hold said bridging contact in fola contact engaging position and comprising a plurality of convolutions one of the longer sides of each of which extends substantially longi tudinally of the path of magnetic fiux between the pole faces of said magnet, the'gradient of said compression spring beingless than the combined gradients of said helical spring and said magnet, and means for supplying electric heating current to said coil and said wire, whereby due to decrease of its magnetic permeability said keeper coil releases said magnet with a snap action to disengage said contacts.

3. An overload relay comprising in combination, a hollow cylindrical base of insulating material closed at one end, a fixed contact mounted, upon said base, a U-shaped permanent magnet slidably mounted within'said base, a movable snap action to disengage said contacts,

4, An overload relay comprising in combination, a hollow cylindrical base of insulating material closed at one end, fixed contacts mounted upon said base, a movable bridging contact extending diametrically of said base, a .U shaped permanent magnet slidably mounted within said base to actuate said bridging contact, a helical spring surrounding said permanent magnet and en aging said base to bias said magnet and said bridglngcontact to a contact disengaging position, a substantially flat current conducting keeper of thermo-magnetic material fixedly attached to said base and disposed opposite the closed end thereof normally to engage the pole faces of said magnet for releasably retaining said magnet in a contact engaging position, and

means for supplying electric heating current to said keeper to reduce the magnetic permeability thereof, whereby with loss ofpermeability said keeper releases said magnet with, a snap action to c said contacts.

5. An overload relay comprising in combination, a hollow cylindrical base of insulatingmaterial, a pair of fixed contacts mounted upon bosses formed exteriorly of said base, a mancompression spring disposed between said bridg ing contact and said reset button to hold said bridging contact in following engagement with said magnet. a helical spring surround ng said permanent magnet and engaging said magnet and said base to bias said magnet to a contact disengaging p ition, a current conducting keeper of thermo-magnetic material fixedly attached to-said base and disposed at the end thereof opposite said reset button, said keeper normally engaging the poie faces of said magnet releasably to retain said magnet in a contact engaging position, the gradient of said compression spring being less than the combined gradients of said helical spring and said magnet, and means for supplying electric heating current to said keeper to reduce the magnetic permeability thereof,

- whereby due to decrease of its permeability said keeper releases said ma net with a snap action to disengage said contacts.

ALLEN G. BI'IMBON. 

